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Starting from rest a 5.0kg block slides 2.5m down a rough 30.0 degree incline in 2.0s.

I know that the PE is 61.3 J. I keep on getting about -57 J when I try to find the mechanical energy lost due to friction but the answer is actually -45 J. Does anyone know what I am doing wrong. This is how I was trying to find it:

W = KEf - PEi

= .5mv^2-mgy

= .5(5.0kg)(2.5m/2.0s)^2 - (5.0kg)(9.8)(sin30*2.5m)